this mod seems to prevent proper saving of circuit signal settings on rail signals.

That sounds very strange. What signals so you mean? Is it the Artillery wagon state when waiting at a rail signal? Or is it interfering with vanilla circuit and rail signal behavior even when no Artillery wagons are present?

when you blueprint or copy any rail signal while this mod is active the rail signal loses it's circuit settings and saves the default ones instead.

ie the red yellow green circuit settings

Okay, that is super weird. I'll look into it.

I don't see it happening in my game. I have just Smart Artillery installed, made a Rail Signal with non-default circuit conditions, made a blueprint of the signal and connecting wires, and placed it down. The new signal had the correct circuit conditions. Even if the blueprint contains an autofiring artillery wagon (which my mod replaces with a normal wagon in the blueprint). Can you send me a save of the game where this happened to you?